もし彼が危険に気づいたなら、安全を確保するためにドアを閉めるだろう.

If he noticed danger, he would close the door to ensure safety.

もしあなたが責任感があれば、家を出る前に鍵でドアを閉めるでしょう。

If you were responsible, you would lock the door with a key before leaving the house.

もし私があなたの立場なら、冷たい空気を遮るためにドアを閉めるでしょう。

If I were in your place, I would close the door to keep out the cold air.